This paper presents the results of a study to evaluate the efficiency of a modified vortex separator (MVS) and an ultraviolet (UV) disinfection unit for direct treatment of combined sewer overflows (CSOs). The MVS included dissolved air and coagulant addition. The effluent from the vortex separator was disinfected continuously using UV light. Bench-scale tests were performed on CSO samples to screen various coagulants and operating pressures for dissolved air. Field tests were performed at the CSO pilot facility where simulated as well as actual storm-generated overflow events were studied.

Performance comparisons between the MVS and other CSO treatment technologies are presented. Results indicate that the MVS achieves pollutant removals superior to conventional sedimentation for the same surface loading rates, or can be hydraulically loaded several times higher than sedimentation to achieve the same results. The results also indicate that the MVS significantly improved solids concentration capability when compared to the conventional operation of the vortex separator. UV disinfection performance was dependent on TSS removal and showed promise for full scale implementation when combined with MVS treatment.

This project was sponsored by the Water Environment Research Foundation and was a collaborative effort between ten participating organizations including the US Environmental Protection Agency (EPA), municipalities, consulting firms and equipment manufacturers.